1,720,965 research outputs found
SEISMIC VULNERABILITY OF INDUSTRIAL STEEL PALLET RACKS: DEVELOPMENT OF FRAGILITY CURVES FOR EXISTING AND RETROFITTED CONFIGURATIONS
No full textLa globalizzazione e l'ascesa dell’e-commerce hanno aumentato in modo significativo la produzione e l'utilizzo dei sistemi di stoccaggio. Questi tipi di strutture sono elementi fondamentali per lo stoccaggio delle merci e svolgono un ruolo importante nella società. Tuttavia, i recenti terremoti italiani (Emilia-Romagna 2012 e Centro Italia 2016) hanno dimostrato in modo drammatico l'elevata vulnerabilità sismica dei sistemi di scaffalatura porta pallet, originariamente concepiti e progettati solo per carichi statici. Sebbene le attuali normative sulle scaffalature contengano chiari requisiti contro le azioni sismiche, la maggior parte delle scaffalature industriali ancora in uso non risulta conforme a tali normative. L'obiettivo di questa tesi è quindi quello di valutare la fragilità sismica di queste strutture, cercando di individuare le principali caratteristiche che le influenzano negativamente soprattutto durante le azioni sismiche.
Innanzitutto, si cerca di definire, attraverso uno studio tassonomico, quali caratteristiche hanno le strutture presenti sul territorio italiano. A tal fine, è stato creato un database contenente circa 120 casi di strutture di scaffalature portapallet distribuite dal Nord al Sud Italia. Dopo averle suddivise in base all'altezza, al numero di livelli e alla presenza o meno di controventature, sono stati scelti 9 casi studio per contribuire alla definizione della vulnerabilità sismica. Per poter analizzare in modo parametrico tutti i casi studio definiti, è stato sviluppato un codice specifico attraverso il software OpenSees, che definisce una modellazione 3D della scaffalatura e implementa le principali non-linearità strutturali dei montanti e delle connessioni, oltre a un modello di attrito per simulare lo scorrimento del pallet. Le scaffalature sono state poi sottoposte a un'analisi non lineare (NLTHA) con 268 accelerogrammi bidirezionali con terreno rigido e soffice. Dopo aver modellato la struttura vengono definiti i parametri di domanda ingegneristica (EDP) utili per determinare le curve di fragilità.
Nell'ultima parte della tesi, vengono effettuate analisi di retrofit sismico su strutture esistenti eseguendo modifiche migliorative alla struttura attraverso tecniche classiche (aggiunta di controventi verticali, miglioramento delle prestazioni di alcuni elementi della struttura) o attraverso tecniche innovative come l'isolamento alla base o il sistema di isolamento di piano.Globalization and the rise of e-commerce have significantly increased the production and use of goods storage systems. These types of facilities are key storage points for goods, playing an important role in society. However, recent Italian earthquakes (Emilia-Romagna 2012 and Centro Italia 2016) dramatically demonstrated the high seismic vulnerability of pallet racking systems, originally conceived and designed for static loads only. Although current racking regulations contain clear requirements against seismic actions, most of the industrial racks still in use today do not comply with these regulations. The aim of this thesis is therefore to assess the seismic fragility of these structures, trying to uncover the main characteristics that negatively affect racks during seismic action.
First of all, an attempt is made to define, through a taxonomic study, which characteristics the structures present in the Italian territory have. In order to do this, a database was created, containing around 120 cases of pallet racking structures distributed from North to South Italy. After subdividing them according to height, number of levels, and the presence or absence of bracing, 9 case studies were chosen to help define seismic vulnerability. In order to be able to analyse all the defined case studies in a parametric way, a specific code was developed in the OpenSees framework, defining a 3D rack modelling, and implementing the main structural non-linearities of the uprights and connections, as well as a friction model to simulate the sliding of the pallet. The racks are then subjected to a Non-Linear Time History Analysis (NLTHA) with 268 bi-directional accelerograms with rigid and soft soil. Then the engineering demand parameters (EDPs) useful for determining the fragility curves are defined.
In the last part of the thesis, seismic retrofit analyses are carried out on existing structures by performing improvement modifications to the structure through classical techniques (adding vertical bracing, improving the performance of certain elements of the structure) or through innovative techniques such as base isolation or load-level isolation system (LLIS)
Evaluation of optimal FVDs for inter-storey isolation systems based on surrogate performance models
Full text linkInter-storey seismic isolation is increasingly gaining attention. One of the main related issues is the need to limit the relative displacement between substructure and superstructure, while maintaining a good seismic performance of the superstructure. As shown in some studies, fluid viscous dampers (FVDs) mounted in isolation systems are effective in reducing isolator deflection but can be harmful by amplifying inter-storey drifts and floor accelerations. Additionally, the effectiveness of FVDs for inter-storey applications was investigated only recently, and specific approaches for their optimisation and performance evaluation are missing. Therefore, this paper proposes a method for the optimal multi-objective design of FVDs, based on the definition of appropriate surrogate response models, which allows for rationally comparing the FVD effects for a wide range of dampers and structures. In particular, the optimal FVD parameters are provided in a dimensionless form, so that they can be predicted by design equations of general validity within the range of the structures analysed. This method is applied to a stock of regular structures with various vibration periods of superstructure, isolation and substructure, examining a linear and a non-linear isolation system and a set of natural records, in order to comprehensively assess the effects of FVDs and their non-linearity on the seismic performance of these structures. Finally, prediction models of optimal FVD parameters are provided based on the results obtained and are applied to three case studies as an example
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Assessment of the inter-story isolation technique applied to an existing school building
No full textInter-story Isolation System (IIS), which combines the functions of seismic isolation and mass damping, is becoming increasingly attractive to mitigate the seismic risk of buildings. This technique is mainly applied in high-rise and multi-purpose buildings, promoting architectural freedom, and representing a sustainable housing solution in densely populated countries. An interesting but still little exploited use of the IIS concerns the addition of isolated stories on top of existing buildings which, beyond increasing the volume and functionality of the buildings, can also reduce their base shear forces and inter-story drifts when the IIS is properly designed. To this end, some design methods are available in the literature based on both frequency and time domain approaches. However, research studies focusing on real case studies are still very few. This paper presents an ideal application of the IIS to an existing two-story RC school building, with the aim of raising it by one story while improving its seismic performance. Firstly, the optimization study of the IIS parameters (frequency and damping ratios) is presented, which is based on a time-history (TH) parametric analysis using the equivalent lumped-mass model, and the optimal solutions are compared with those from other general approaches in frequency domain. Then, the effectiveness of the optimal IIS in improving the seismic performance of the school building is evaluated by comparing the TH responses of the associated 3D finite element models, with and without IIS, under a set of spectrum- compatible bidirectional natural records. Ultimately, the results obtained confirm the effectiveness of the IIS and promote it as a potential seismic retrofit technique, even if specific case-by-case assessments are required
Seismic fragility of unbraced industrial steel pallet racks
Full text linkPast Italian earthquakes revealed the high seismic vulnerability of steel pallet racks designed for gravity loads only, which are still the most widespread industrial storage system. This study aims to derive the seismic fragility of these structures to enable more refined estimates of enterprise risk and the definition of effective retrofit solutions. For this purpose, 3D non-linear models of 27 unbraced pallet racks, representative of the Italian context, were analysed in Time-History under 268 bidirectional events, representative of Italian seismicity. Multiple fragility models were then derived, based on various engineering demand parameters and seismic intensity measures, through a cloud approach
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